This invention relates to a method for automatically setting signal processing conditions so as to obtain finished images in a desired manner in a color image input/output system.
In a color image input/output system is generally employed a method of reading color originals for color separation by an image input device (e.g. color scanner), processing such input density signals of respective colors from the device in gradation, and inputting thus processed density signals of respective colors into an image output device (e.g. laser color printer). More specifically, input density signals are processed by using a density histogram prepared with pixel data to determine the highlight density, shadow density and gradation conversion curves in the system. The gradation conversion curves are set generally based upon the concept of unifying density histogram values in output images thereby to incapacitate faithful reproduction of the images of the original. For instance, the images which are in high-key or low-key in the original come out in normal tone in the output images. Moreover, it is difficult to automatically set high-light density when the original has a relatively large catch light point or has no high-light points. Mistakes are often caused in such a case. It is difficult to set gradation for retouching color fogging or other defects.